Permanent magnets are typically used in which application?

Permanent magnets are primarily utilized in applications where a constant magnetic field is required without the need for external power sources. In the context of the given options, small portable alternators make effective use of permanent magnets. These alternators can produce electrical energy efficiently and are often lightweight and compact, making them ideal for portable applications where space and power are limited.

Induction motors, series motors, and shunt motors usually rely on electromagnetic windings to create magnetic fields, which allows for more versatile operation and control. In contrast, small portable alternators leverage the stability and simplicity of permanent magnets to generate electricity efficiently, ensuring a steady output in compact designs. This makes them a popular choice for portable power applications.